Infrared (IR) detectors used in IR cameras, IR guidance systems for missiles, and the like require a thin metal shield to surround the detector. The shield, sometimes referred to as a cold shield or radiation shield, protects the detector from stray IR radiation. The shield typically has an aperture in the top to allow a prescribed cone of light to strike the detector contained within the shield.
Cold shields are often made by electrodepositing nickel, copper, nickel-cobalt, or combinations of such metals onto an aluminum mandrel. Often, the aluminum mandrel is coated with a zinc deposit and/or copper strike prior to the actual forming so that the electrodeposited metal will adhere to the mandrel surface and thereby prevent loss of adhesion during electrodeposition on post-plate machining. After the electrodeposition operation is complete and post-plate machining accomplished, the aluminum mandrel is dissolved, e.g., in an alkaline solution such as sodium hydroxide. The zinc and/or copper strike coating is then stripped off the interior of the shield once the mandrel has been dissolved.
The shields are ordinarily coated on the outside surface with gold or other materials that are reflective to IR radiation. The shields are generally coated on their interior surfaces with materials that are absorbent to IR radiation. Such interior and exterior coatings are used to minimize the amount of stray IR radiation impinging on the detector.
As can be appreciated, there is an ongoing need to improve the accuracy of IR detectors, and hence to reduce the amount of stray IR radiation hitting the detector.